JPH052085B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a strain gauge type load cell mainly used in a scale.

(Prior art) A load cell used for weighing, etc. is configured to electrically detect the amount of strain in a strain body corresponding to an applied load using a strain gauge attached to the strain body. However, especially for load cells for scales that are often used in environments with a lot of moisture and humidity, it is necessary to protect the strain gauges from moisture and moisture in order to obtain the required durability. Therefore, in the past, strain gauges have been subjected to moisture-proofing treatments such as being coated with a polymeric material such as silicone rubber, butyl rubber, or polyurethane, or being sealed with metal foil.

However, according to these moisture-proof treatments, the covering material such as a polymeric material or metal foil is directly adhered to the strain gauge, so that the expansion and contraction of the strain gauge due to the deformation of the strain body is restricted by the covering material. As a result, the amount of strain on the strain-generating body, that is, the applied load, cannot be detected correctly, and these covering materials in particular become a cause of creep errors. Figure 8 shows the results of an experiment regarding this creep error, in which the output voltage of the load cell was measured when a load of 10 kg was applied for 10 minutes. This is the output of a load cell whose strain gauge is directly covered with silicone rubber. As can be seen from Fig. 8, the output of a load cell whose strain gauge is coated with silicone rubber is limited by the strain induced when a load is applied or unloaded because the expansion and contraction of the strain gauge is restricted by the silicone rubber. The response to body strain is poor, and as time passes, the output changes to approach that of a load cell that has not been coated, and only reaches the normal output value after a certain period of time. Therefore, the output value will not correctly indicate the load value before a certain period of time has elapsed. In addition, the creep characteristics as mentioned above are
This varies depending on the application method and amount of coating material such as silicone rubber that covers the strain gauge, which causes variations in accuracy between load cells.

(Object of the Invention) The present invention deals with the above-mentioned problems in a load cell in which a strain gauge is attached to a flexure element. The object of the present invention is to improve the durability of the load cell without reducing the accuracy of the load cell or causing creep errors.

(Structure of the Invention) That is, the load cell according to the present invention has a structure in which a strain gauge is attached to a low-rigidity portion provided on a strain-generating body, and the strain gauge is coated with a polymeric material. A fluorine-based polymer that does not have adhesive properties to the polymeric material is thinly applied thereon, and the strain gauge and the fluorine-based polymer are then covered with the polymeric material. do.

According to this configuration, the fluorine-based polymer is applied extremely thinly compared to a coating material such as silicone rubber, so even if it is directly adhered to the strain gauge, it does not hinder the expansion and contraction of the strain gauge. Moreover, since it has no adhesive property at all to the polymer material coated on top of it, the strain gauge is not bound to silicone rubber or the like via the fluorine-based polymer.

In addition, examples of the above-mentioned fluorine-based polymers include:
Florado, Futargient (both product names)
etc. are used.

(Example) The present invention will be described below based on an example shown in the drawings.

Fig. 1 shows a load cell used in a scale, and the load cell 1 is supported in a cantilevered manner via brackets C and D between a scale body A and a weighing pan B provided on its upper part. , the weight of the object to be weighed placed on the weighing pan B is applied to one end. Next, the configuration of the load cell 1 will be explained with reference to FIG. 2. The strain body 2 that is the main body of the load cell 1 includes a fixed rigid body part 3 at one end that is fixed to the scale body A via the bracket C, and A movable rigid part 4 at the other end to which the weighing pan B is fixed via the bracket D, and an upper beam part 5 and a lower beam part 6 provided between the upper and lower ends of both rigid parts 3 and 4.
It has a hollow four-sided shape. The upper beam part 5 and the lower beam part 6 are each formed with two low-rigidity parts 5b and 6b whose wall thickness is reduced by semicircular cuts 5a and 6a, and each of the low-rigidity parts Parts 5b, 5b, 6b, 6b
Strain gauges 7...7 are adhered to the surfaces of each. As shown in FIGS. 3 and 4, the strain gauge 7 has a resistance wire 9 made of foil arranged in a meandering manner on a base 8, and a cover 10 covering the resistance wire 9. It has a configuration in which lead wires 11 are connected to both ends.

However, as shown in FIGS. 3 and 4, a fluorine-based polymer 12 that does not have adhesive properties to silicone rubber is thinly coated on top of each strain gauge 7, and the fluorine-based polymer 12 is applied on top of this. A silicone rubber 13 is coated by coating or dipping so as to completely cover the polymer 12.

According to the above structure, each low rigidity portion 5 of the strain body 2
The strain gauges 7...7 attached to the surfaces of the silicone rubber 13, 1
3 will protect it from water and humidity. On the other hand, a fluorine-based polymer 12 is interposed between each strain gauge 7 and the silicone rubber 13, but the fluorine-based polymer 12 is applied extremely thinly and is adhesive to the silicone rubber 13. Therefore, each strain gauge 7 is not prevented from expanding and contracting by the fluorine-based polymer 12, and is separated from the silicone rubber 13. Therefore, when an object to be weighed is placed on the weighing pan B shown in FIG. When the surfaces of the low-rigidity parts 5b, 5b, 6b, 6b are expanded or contracted, each strain gauge 7...7 attached to the surface of the low-rigidity parts 5b, 5b, 6b, 6b is made of silicone rubber. 1
3 and 13, and expands and contracts faithfully following the expansion and contraction of the surfaces of the low-rigidity parts 5b, 5b, 6b, and 6b. As a result, the strain amount of the strain body 2, ie, the weight of the object to be measured, can be detected with high precision as the electrical output from the strain gauges 7...7.

Next, a second embodiment of the present invention shown in FIGS. 5 to 7 will be described.

As shown in FIGS. 5 and 6, the strain body 22 of the load cell 21 in this embodiment has a fixed rigid body part 23 at the lower end and a movable rigid body part 24 at the upper end to which a load is applied.
and a small-diameter low-rigidity portion 25 provided between both rigid body portions 23 and 24 in a column shape, and a plurality of strain gauges 26 are arranged around the low-rigidity portion 25.
...26 is pasted. Then, a low rigidity portion 25 is provided so as to cover each strain gauge 26...26.
A fluorine-based polymer 27, which does not have adhesive properties to silicone rubber, similar to that of the first embodiment, is thinly coated on each of the rigid body parts 2.
3, 24 and a silicone rubber layer 28 covering the entirety of the low-rigidity portion 25. Here, the contact surface with the silicone rubber layer 28 on the circumferential surface of each of the rigid body parts 23 and 24 is physically roughened or treated with a primer to increase the adhesion force with the silicone rubber layer 28. This is designed to effectively prevent moisture from entering the bonded portions of the strain gauges 26...26.

Also in this embodiment, since the fluorine-based polymer 27 is interposed between each of the strain gauges 26...26 and the silicone rubber layer 28, the strain gauges 26...26 are connected to the silicone rubber layer 28. Therefore, the strain of the low-rigidity portion 25 corresponding to the load can be detected with high accuracy.

Note that the silicone rubber layer 28 in this example
is formed, for example, by a potting method as shown in FIG. In other words, the rigid body parts 23 and 24 are subjected to primer treatment or surface roughening treatment, and the low rigidity part 25 is treated with a strain gauge 2.
6...The flexure element 22 coated with the fluorine-based polymer 27 is set in the pot-shaped mold 30 so as to cover the fluorine-based polymer 27, and then two liquids, a base material and a curing agent, are applied around the flexure element 22. Pour the mixed thermosetting silicone rubber. Then, the silicone rubber is cured by heating at about 100°C for about 1 hour, and then the mold 30
Remove the product from the As a result, a load cell 21 as shown in FIGS. 5 and 6 is obtained.

(Effects of the Invention) As described above, according to the present invention, in a load cell in which a strain gauge is attached to a low-rigidity portion provided on a strain-generating body, a polymer material such as silicone rubber is placed on the strain gauge. The structure is such that a fluorine-based polymer that does not have adhesive properties is applied thinly to the surface of the body, and then a polymeric material is coated on top of the thin film. The polymeric material protects the material from water and moisture without being constrained by the material. As a result, a load cell with excellent durability and high weighing accuracy can be realized as a load cell for a scale that is often used in an environment with a lot of moisture or humidity.

[Brief explanation of the drawing]

FIG. 1 is a front view showing one usage state of the load cell according to the first embodiment of the present invention, FIG. 2 is a front view of the load cell alone, and FIGS. 3 and 4 are enlarged plan views and essential parts of the load cell. 5 is a vertical sectional front view showing a load cell according to a second embodiment of the present invention, FIG. 6 is an enlarged cross-sectional view taken along the line of FIG. 5, and FIG. 7 is an enlarged longitudinal sectional view of the embodiment. It is an explanatory view showing one manufacturing process of the load cell concerning this. Further, FIG. 8 is a graph showing the creep characteristics of the load cell, which shows the conventional problem. 1, 21... Load cell, 2, 22... Strain body, 5b, 6b, 25... Low rigidity part, 7, 26...
...Strain gauge, 12,27...Fluorine polymer, 13,28...Polymer material (silicone rubber, etc.).

Claims (1)

[Claims] 1. A load cell in which a strain gauge is attached to a low-rigidity portion provided on a strain-generating body, and the strain gauge is covered with a polymeric material, and a strain gauge is provided on the strain gauge, and a strain gauge is coated with a polymeric material. 1. A load cell characterized in that a non-adhesive fluorine-based polymer is thinly applied on the strain gauge and the fluorine-based polymer is coated thereon with the above-mentioned polymeric material.